Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of the first image of a display screen or portionthereof with a transitional graphical user interface showing the newdesign.

FIG. 2 is a second image in a sequence thereof.

FIG. 3 is a third image in a sequence thereof; and,

FIG. 4 is a fourth image in a sequence thereof.

Within the drawings, the appearance of the transitional imagesequentially transitions between the embodiments shown in FIG. 1 throughFIG. 4. No ornamental aspects are associated with the process or periodin which one image transitions to another image. The outermost brokenlines illustrate the display screen or portion thereof and form no partof the claimed design. The remaining broken lines illustrate portions ofthe graphical user interface and form no part of the claimed design.

CLAIM The ornamental design for a display screen of portion thereof witha transitional graphical user interface, as shown and described.